T. S. Zhao Chair Professor of Mechanical & Aerospace Engineering Director of the HKUST Energy Ins@tute Senior Fellow of the HKUST Ins@tute for Advanced Study
Use of fossil fuels vs. Environmental problems Electricity Vehicles Heat Engines NOx, SOx CO 2 Par@culates Combus@on O 2 Fuel
Sustainable Energy Future Wind Solar Biomass Electricity Heat Biofuels Electrical Thermal Fuel Cells Energy Storage Energy Storage Utilization: Consumers need motion, sound, light, heat, communication
Fuel Cells
Fuel cell is clean Hydrogen Methanol Ethanol AIR methane Heat Fuel Cell Electricity Water Clean products
Fuel cell is efficient
Fuel cell is scale Anode catalyst Cathode catalyst H 2 O 2 Stack of several hundred Electrolyte frame Bipolar plate
Fuel cell is enabling technology
Our Fuel Cell Research Alcohols Biogas Direct Solid Oxide Alcohol Fuel Cell Fuel Cell (SOFC) e - e -
Direct Alcohol Fuel Cells
Alcohols have high energy density 2 ml 360 ml 0.6 ml 0.2 ml 0.4 ml Methanol Hydrogen – Liquid Hydrogen Li-ion & Ethanol uncompressed gas Hydrogen from BaVery Chemical Hydride Fuel Volume per WaV hour
DMFC is a carbon neutral, sustainable tech n Opera@ng at room temperature n Quiet & no moving parts
Issues with DMFC Performance is low : a decade ago, 30-50 mW/cm 2 1.15 Catalyst ac@va@on loss Voltage loss Ion transport loss Voltage, V Mass transport loss Polariza@on curve V cell I cell Current density
Complexity in the fuel cell process Gas Liquid Gas Liquid Catalyst layer (nanoscale) Diffusion layer (microscale) Flow channel (macroscale) Reac@ons (e-, H+, Heat…); Rate (T, C); Transport (mul@- component, Mul@-phase); Structure (Mul@-scale..)
Our Approach Int J Heat Mass Transfer, 47 (2004) Flow behavior Current 5725-5739. Journal of Power Mass transport Current Sources, 139(1-2) Experimenta@on 79-90. Electrochemistry Heat transport Mass transport Communica@ons 7 (2005) 288-294. Current Electrochimica Acta Theore@cal framework Theory 52 (2007) 6125-6140 Experimenta@on Revealing intricacy of cell opera@on + & Improving cell performance Simula@ons
Breakthrough: DMFC performance boost
Breakthrough: DMFC performance boost 0.75 250 16.5 wt.% PTFE 11.7 wt.% PTFE 8.0 wt.% PTFE 200 3.8 wt.% PTFE 2 non-wetproofed Power density, mW/cm 0.50 Cell voltage, V 150 100 0.25 50 0 0 0 200 400 600 800 1000 1200 Current density, mA/cm 2 Power density (200 mW/cm 2 ) J Power Sources 171 (2007) 268-274
Innova@on: High-performance DMFC electrode Energy & Environmental Science, 4, 1428-1433
Breakthrough: Direct ethanol fuel cell Now Previous World-record power density: 180 mW/cm2 J Power Sources 187 (2009) 387-392 Energy & Environmental Science 2012,5,5333-5339
Discovery: DMFC Opera@on H2 Electrochemical and Solid-State LeVers, 8 (1) A52-A54 (2005)
Discovery: DMFC Opera@on H2 Electrochemical and Solid-State LeVers, 8 (1) A52-A54 (2005)
Implica@ons A new method for hydrogen produc@on — Instant — Applicable at room temperature — No CO species
Our prototypes…
10 hours on 5-cc fuel
Solid Oxide Fuel Cells (SOFC)
SOFC is a clean, carbon neutral, efficient tech n Ceramic electrolyte n High efficiency (~70%) conduc@ng oxygen ions n No combus@on; clean n High temperature (700 o C); n Fuel flexibility inexpensive catalysts
Biogas from sewage sludge in HK Sludge treatment works in HK produce biogas for 9.7 Million m 3 (2014) Biogas composi@on Average percentage% CH 4 65 CO 2 35 H 2 S(ppm) 100-4075 Others(%) -
Current biogas u@liza@on Biogas: 9.7 Million m 3 Heat Engines ( η = 30%-40%) Biogas water boiler at Tai Po STW Electricity: 2.35-3.12×10 10 W-hour Dual fuel engine generator at Sha Tin STW ~3500 people CHP generator at the Shek Wu Hui STW
Change to SOFC Biogas: 9.7 Million m 3 SOFC ( η = 70%-75%) Electricity: 5.48-5.86×10 10 W-hour Added benefits: — Clean (no NOx, no SOx) — Quite opera@on ~7000 people — Compact system
Challenging issue: Carbon deposi@on Mechanisms: n Breaking down C-H bonds @Nickel catalyst → free radicals n CH 4 →C+2H 2 n Polymeriza@on of free radicals n Deposi@on in pores of the anode Deposited C filament Ni-YSZ anode
Challenging issue: Sulfur poisoning n Auer desulfuriza@on, ~ppm level H 2 S can lead to cell performance degrada@on. n Commercial electrodes can only withstand 2 ppm H 2 S Mechanism of sulfur poisoning Int J of Hydrogen Energy 33 2008 6316 Energy & Environ. Sci 4 2011 4380
SOFC demos with biogas from anaerobic diges@on sludge treatment Loca>on Scale Remarks Year Spain 5 kW e No external biogas reforming 2009-2011 Germany 1 kW e External reformer 2014 Italy 175 KW e External reformer Under construc@on
Our Strategies: reforming SOFC Dry reforming △ H o =206 kJ/mol Biogas CH 4 +CO 2 →2CO+2H 2 H 2 +O 2- →H 2 O+2e - ( ~65% CH 4 , 30% CO 2 , 0.3% CO) H 2 O + CO 2 CO+O 2- →CO 2 +2e - Steam reforming △ H o =247.3 kJ/mol Biogas + Steam CH 4 +H 2 O→CO+3H 2 H 2 +O 2- →H 2 O+2e - ( ~65% CH 4 , 30% CO 2 , 0.3% CO, H 2 O) H 2 O + CO 2 CO+O 2- →CO 2 +2e - Par@al oxida@on △ H o =-35.6 kJ/mol Biogas + O 2 CH 4 + 1/2O 2 → CO + 2H 2 H 2 +O 2- →H 2 O+2e - ( ~65% CH 4 , 30% CO 2 , 0.3% CO, O 2 ) H 2 O + CO 2 CO+O 2- →CO 2 +2e -
Our Strategies: reforming H 2 H 2 CO CO CO 2 CO 2 CH 4 Biogas Biogas CH 4 Biogas External Reformer H 2 O Anode side Anode side Reformer H 2 O Anode side H 2 O Cathode side Cathode side Cathode side Air Air Air External reforming-SOFC Indirect internal reforming-SOFC Direct internal reforming-SOFC (ER-SOFC) (IIR-SOFC) (DIR-SOFC) or direct biogas-SOFC n DIR-SOFC is more energy efficient with the highest heat u@liza@on. n Steam produced on the DIR-SOFC anode will help facilitate the anode reac@on. J Power Sources 142 2005 75 J Eng. Gas Turbines Power 127 2005 86
Our strategies: S tolerant anode Find good electrode materials that can tolerate S to generate high power output with improved durability. p Ni-based cermet anode with YSZ replaced by other oxygen ion conductors; p Cermet anodes with Ni replaced by other metals; p Conduc@ve metal oxides: such as Sr 2 MnMoO 6-δ .; Sr 2 MgMoO 6-δ .
Strategies: S tolerant anode Ni-YSZ with Ni par@ally replaced by n Conduc@ve metal oxide anodes other metals n On oxide anode materials there is reduced S adsorpEon. 800 ºC, H 2 S 20 ppm Cu-ceria anode n Fast oxygen ion conducEon might enhance S removal Electrochemical and Solid-State LeJers , 8 2005 A279 Applied Catalysis A: General 486 2014 123 Science 254 2006 312
Study of La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3−δ impregnated anodes C deposi@on on cell-5 @ Ni-YSZ anode cell-1: a cell with 5 wt.% LSCrM-impregnated YSZ anode; cell-2: a cell with 35 wt.% LSCrM-impregnated YSZ anode; cell-3 a cell with 32 wt.% LSCrM+6wt.% Ni + 2wt.% Ag-impregnated YSZ anode; cell-4: a cell with 32 wt.% LSCrM and 6 wt.% Ni impregnated YSZ anode cell-5: a cell with 30 wt. % Ni impregnated YSZ anode
Our Biogas SOFC Experimental Setup Power output MFC Electrochemical Interface & MFC Impedance Analyzer MFC Temperature control system MFC SOFC Temperature controller CO CO 2 CH 4 H 2 S T H 2 O Evaporator recircula@on Peristal@c pump Tailgas treatment Tailgas Gas flow control system system analyzer Cell opera@ng temperature: 600-800 o C
Summary and Outlook n Fuel cell is an enabling technology to increase the use of clean and renewable energies and to address climate change and air pollu@on problems. n We have made breakthroughs in direct alcohol fuel cells. n Solid oxide fuel cells offer the promise to convert biogas from sewage sludge treatment to electricity in a cleaner way with much higher efficiency. n We will address the issues with the use of biogas in solid oxide fuel cells (carbon deposi@on and sulfur poisoning)…
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